Nonseizing article of aluminum and method of producing the same



Patented Oct. 23, 1934 UNITED STATES NONSEIZING ARTICLE OF ALUMINUM METHOD or PRODUCING THE SAME Seth G. Malby, Tenafly, N. J., assignor, by mesne assignments, to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application February 1, 1932, Serial No. 590,325

4 Claims.

This invention relates to methods for producing on aluminum articles a coating which will prevent the aluminum article from seizing or sticking to the surface of another aluminum arti- 5 cle with which it is in contact under pressure.

The invention further relates to non-seizing aluminum articles. The invention is equally applicable to aluminum or aluminum base alloys, but for the purposes of description the word aluminumi will be used herein and in the appended claims as describing both aluminum and aluminum base alloys.

It is well known in the art that two aluminum surfaces in contact under high pressure may "seize or stick one to the other in such manner as to practically preclude normal movement between them. For instance, in the case of screw machine articles, such as aluminum bolts, nuts,

and the like, where a threaded aluminum article is designed to work upon a complementary threaded article also made of aluminum, this problem of seizing becomes acute. I Likewise, without proper surface treatment it is impossible to make aluminum valves which can successfully be used with aluminum seats. Generally the problem of the prevention of aluminum articles from seizing is a serious one.

To .avoid the seizing of aluminum articles many compositions and many methods of surface treatment have been proposed. Of the compositions proposed a few have been found workable, but in general such compositions are unsatisfactory because they produce greasy surfaces which are not desirable when aluminum is used in the handling of foods, for example, and also because the compositions used are often such that they are readily wiped off the aluminum surface. Among the surface treatments proposed for the provision of non-seizing aluminum articles, the treatment described in U. S. Patent 1,661,448 to C. S. Taylor is outstanding. However, the dense adherent coating of aluminum oxide proposed in this patent is not entirely satisfactory for all purposes.

The principal object of the present invention is to provide a non-seizing aluminum article which has a clean surface and which, particularly in its preferred form, is capable of retaining a non-seizing surface over long periods of use. A further object of the invention is to provide methods by which the above object may be attained, which methods are simple in execution.

I have discovered that if aluminum is provided with a coating of a metal stearate, an article is produced which has non-seizing properties well in advance of any non-seizing aluminum article heretofore used by the art. I have further discovered that while a coating of a metal stearate may be applied to any aluminum or aluminum base alloy article, the full benefits of the coating are best realized when it is placed upon aluminum which has on its surface what is commonly known to the art as an oxide coating.

The oxide coatings I have in mind are of appreciable thickness, are composed substantially of aluminum oxide, are hard in nature, and adhere effectively to the metal. Such coatings may be produced artificially by several methods, among the most successful of which are those methods which comprise making the article to be coated the anode in an electrolytic cell, the electrolyte of which is a solution of sulfuric acid, or a solution of chromic acid or one of the various solutions described by the art for such purposes. Another successful method consists in dipping the aluminum into a hot solution of an alkali chromate and an alkali carbonate. These methods, which form no part of the present invention, are well known to the art and need not further be described.

The method of applying the stearate which has proved most satisfactory in the practice of my invention consists in dipping the aluminum article to be treated in a molten bath of a metal stearate. Of the metal stearates, zinc stearate is, I have found, the most effective in imparting anti-seizing properties to the aluminum and I generally prefer in the practice of my invention to use a bath of molten zinc stearate. The aluminum article, after being dipped in the molten stearate, is then removed from the bath and is ready for use. I prefer to maintain the bath at the lowest temperature possible in order to avoid unduly heating the aluminum article since many aluminum articles, and particularly those made of aluminum alloys, have properties which may be impaired if the bath is at too high a temperature or if the article is immersed in the bath for long periods.

Aluminum articles which have been coated with a metal stearate, and particularly with zinc stearate, by the method above described do not readily seize when they bear, under pressure, upon the surface of another aluminum article.

Likewise, the coating thus formed upon the aluminum is comparatively durable.

When, however, it is desired to treat an aluminum article which is designed to be permanently installed in such a position as to have relative movement with respect to another aluminum article and to bear upon the surface thereof, I prefer to first provide the aluminum article with an oxide coating and to dip the oxide-coated article in the molten stearate in the manner hereinabove mentioned to obtain a film of metal stearate on its oxide-coated surface. An article thus formed is superior in its non-seizing properties to the article described in the aforesaid patent to Taylor, and is likewise superior to all non-seizing surfaces heretofore known in that it is substantially permanent, and the non-seizing property of the coating does not, under normal wear, disappear.

Another advantage of non-seizing aluminum articles coated with metal stearate is that there is upon the surface no loose material or grease which will be readily loosened by the flowing action of liquids or the like and contaminate the solution with which the aluminum article is in contact. My invention is, therefore, particularly advantageous in connection with aluminum valves having aluminum seats which are used to control the passage of liquids and solutions.

Although I have described my invention with reference to particular features and details, the invention is not limited to the features specifically described except as in the appended claims.

I claim:

1. A method of making a non-seizing aluminum article consisting in dipping the article in a bath of molten zinc stearate.

2. A method of making a non-seizing aluminum article comprising forming on the surface of said article an oxide coating, and thereafter immersing the oxide-coated article in a bath of molten metal stearate. and removing said article from said bath.

3. A method of making a non-seizing aluminum article comprising forming on the surface of said article an oxide coating, and thereafter immersing the oxide-coated article in a bath of molten zinc stearate, and removing said article from said bath.

4. A non-seizing aluminum article, the surface of which is provided with a lubricating oxide coating of appreciable thickness and a film of metal stearate.

SETH G. MALBY. 

